The Zappa-Szép product of twisted groupoids

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Hauptverfasser: Duwenig, Anna, Li, Boyu
Format: Preprint
Veröffentlicht: 2024
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author Duwenig, Anna
Li, Boyu
author_facet Duwenig, Anna
Li, Boyu
contents We define and study the external and the internal Zappa-Szép product of twists over groupoids. We determine when a pair $(Σ_{1},Σ_{2})$ of twists over a matched pair $(\mathcal{G}_{1},\mathcal{G}_{2})$ of groupoids gives rise to a Zappa-Szép twist $Σ$ over the Zappa-Szép product $\mathcal{G}_{1}\bowtie\mathcal{G}_{2}$. We prove that the resulting (reduced and full) twisted groupoid C*-algebra of the Zappa-Szép twist $Σ\to \mathcal{G}_{1}\bowtie\mathcal{G}_{2}$ is a C*-blend of its subalgebras corresponding to the subtwists $Σ_{i}\to \mathcal{G}_{i}$. Using Kumjian-Renault theory, we then prove a converse: Any C*-blend in which the intersection of the three algebras is a Cartan subalgebra in all of them, arises as the reduced twisted groupoid C*-algebras from such a Zappa-Szép twist $Σ\to \mathcal{G}_{1}\bowtie\mathcal{G}_{2}$ of two twists $Σ_{1}\to \mathcal{G}_{1}$ and $Σ_{2}\to \mathcal{G}_{2}$.
format Preprint
id arxiv_https___arxiv_org_abs_2406_00466
institution arXiv
publishDate 2024
record_format arxiv
spellingShingle The Zappa-Szép product of twisted groupoids
Duwenig, Anna
Li, Boyu
Operator Algebras
46L55, 46L05, 22A22
We define and study the external and the internal Zappa-Szép product of twists over groupoids. We determine when a pair $(Σ_{1},Σ_{2})$ of twists over a matched pair $(\mathcal{G}_{1},\mathcal{G}_{2})$ of groupoids gives rise to a Zappa-Szép twist $Σ$ over the Zappa-Szép product $\mathcal{G}_{1}\bowtie\mathcal{G}_{2}$. We prove that the resulting (reduced and full) twisted groupoid C*-algebra of the Zappa-Szép twist $Σ\to \mathcal{G}_{1}\bowtie\mathcal{G}_{2}$ is a C*-blend of its subalgebras corresponding to the subtwists $Σ_{i}\to \mathcal{G}_{i}$. Using Kumjian-Renault theory, we then prove a converse: Any C*-blend in which the intersection of the three algebras is a Cartan subalgebra in all of them, arises as the reduced twisted groupoid C*-algebras from such a Zappa-Szép twist $Σ\to \mathcal{G}_{1}\bowtie\mathcal{G}_{2}$ of two twists $Σ_{1}\to \mathcal{G}_{1}$ and $Σ_{2}\to \mathcal{G}_{2}$.
title The Zappa-Szép product of twisted groupoids
topic Operator Algebras
46L55, 46L05, 22A22
url https://arxiv.org/abs/2406.00466